Mobile communication indoor omni-directional ceiling antennas, as a main antenna type for indoor wireless signal coverage, are widely used in indoor distribution systems, of which performance and quality have direct effects on quality of indoor wireless communications and investment efficiency of the indoor distribution system. The omni-directional ceiling antenna generally applies half-wave dipole principles, using a structure of a conical oscillator with a reflecting plate. The conical oscillator can extend impedance bandwidth of the antenna, and existing domestic omni-directional ceiling antennas also use impedance matching lines (sheets) connected between the radiation oscillator and the reflecting plate to reduce size and further extend bandwidth at lower frequency, which can satisfy a requirement that a voltage standing wave ratio (Voltage Standing Wave Ratio; VSWR for short) is less than 1.5 both in 806-960 MHz (low frequency band) and 1710-2500 MHz band or a wider frequency range. However, existing omni-directional ceiling antenna products do not take radiation pattern bandwidth properties into consideration, and have common technical defects, such as downward signals aggregation, i.e. high gains at small radiation angles and low gains at large radiation angles, and poor roundness of radiation pattern in the frequency band of 1710-2500 MHz. These defects in combination with loss characteristics that radio signals attenuate with frequency and propagation distance, result in that signals at a high frequency band, such as that of 3G and 4G, have strong electromagnetic radiation just under the antennas, and coverage thereof is far smaller than signals at a low frequency band, such as that of 2G. In fact, for indoor omni-directional ceiling antennas, a large radiation angle of 85° (taking vertically down as 0°, similarly hereinafter) is generally corresponding to the maximum coverage radius edge, and a small radiation angle of 30° is corresponding to a small vicinity area under antennas. In an indoor signal coverage scenario, it is expected that signal strength at the coverage radius edge should be strong enough to make the coverage more effective; and signal strength just under antennas should be as weak as possible to reduce the electromagnetic radiation. Thus, gains of indoor omni-directional antennas need to be modified by the radiation angle, so that properties thereof can be expounded exactly. High gain means strong coverage capacity at a large radiation angle, but strong radiation at a small radiation angle, whereas low gain means weak coverage capacity at a large radiation angle, but low electromagnetic radiation at a low radiation angle.
In order to solve problems described above, an omni-directional ceiling antenna with improved technique, which has special structures and certain dimensions of a cone-cylinder monopole and a discone reflecting plate without any impedance matching line(s), has been provided. The antenna improved radiation pattern properties at high frequency, ensured complete axial symmetry, and solved the problems of downward signals aggregation and poor roundness of radiation pattern in the frequency band of 1710-2500 MHz. The gain at a small low radiation angle of 30° is significantly reduced by 7-15 dB, the gain at a large radiation angle of 85° is increased by 3-6 dB, and both radiation pattern bandwidth and impedance bandwidth exceed 102%, which greatly improved coverage efficiency of high frequency signals, such as that of 3G.
However, with deployment of higher frequency networks, such as LTE/4G, the above omni-directional ceiling antenna with improved technique could not consider the problem of downward signals aggregation for even higher frequencies in LTE/4G. The radiation angle of maximum gain for frequencies above 2500 MHz directs about 60°, and the gain at 85° is reduced by up to 2 dB or so. The downward signals aggregation is still obvious which causes inefficient coverage of signals and high radiation just under the antenna at even higher frequencies in LTE/4G.